Effect of Ca content on property and structure of SiC/Al foam composites

The effects of Ca content on SiC dispersity in SiC reinforced aluminum matrix(SiC/Al) composites, and the effects of Ca content on the compressive property as well as the structure of SiC/Al foam composites prepared by gas injection method were investigated. Firstly, the SiC/Al composites with different Ca contents were prepared as base materials for the fabrication of SiC/Al foam composites, and the compressive test was conducted to the SiC/Al foam composites with different Ca contents. Then the effects of Ca content on SiC dispersity in the SiC/Al composites and foam structure were analyzed using OM, SEM and XRD. The results show that the addition of Ca can obviously affect the SiC distribution in the SiC/Al composites and there is a critical value of Ca content. SiC distributes uniformly in matrix when Ca content is smaller than 1.5wt%. Intermetallic compounds Ca₂Al₄Si₃ which are rich of Al, Ca and Si form in the melt when Ca content reaches or exceeds 1.5wt%. Their volume fraction and size increase obviously with the increasing of Ca content, which leads to the aggregation of SiC in these intermetallic compounds and their boundaries, affecting the uniformity of SiC distribution. The compressive test reveals that the plateau stress and the compressive yield strength of the compressive stress-strain curves for SiC/Al foam composites have an increasing tendency with Ca content increasing. The corresponding cell wall thickness of SiC/Al foam composites also increases obviously with the increasing of Ca content. It is not only related to the melt viscosity improved by the formation of intermetallic compounds, but more likely related to the size of intermetallic compounds in the melt increasing with the increasing of Ca content.